This invention relates generally to a machine and method for lifting a massive object such as a coil of steel, but the machine can also be readily adapted through the use of conventional fork lift tines, for example, for lifting other objects such as palletized materials, machinery and so forth.
More specifically, this invention relates to a mobile machine and method employing a primary hydraulic cylinder to transfer hydraulic fluid, under pressure, therefrom to one or more secondary hydraulic lifting cylinders, at the same time and in equal proportions, upon operation of the primary cylinder by an auxiliary lifting device, such as a fork lift truck with its lifting tines removed, to thus operate the secondary cylinder(s) to lift a massive object with a force which is a multiple of an input force supplied to the machine by the auxiliary device.
There are many lifting machines, such as fork lift trucks, for example, which are known and used in the prior art which employ more than one hydraulic cylinder to lift massive objects. See, for example, U.S. Pat. No. 3,208,556 issued to W. M. Shaffer on Sep. 28, 1965; U.S. Pat. No. 3,534,664 issued to B. I. Ulinski on Oct. 20, 1970; and U.S. Pat. No. 4,018,307 issued to B. C. Ehrardt, et al. On Apr. 19, 1977, to mention but a few. The machines of Shaffer and Ulinski each employ a plurality of hydraulic cylinders which can be operated sequentially to lift and lower separately movable mast sections, with the forward most mast section containing a vertically movable fork lift carriage and with each movable section carrying one of the cylinders. Ulinski's machine includes a group of cylinders whose piston chambers are hydraulically connected in series wherein each cylinder is operated to lift the remaining cylinders in sequence with the forward most cylinder being operated to lift the fork lift carriage. Shaffer's machine employs cylinders which are series connected mechanically, but not hydraulically, by means of roller guides mounted on piston rods and a different chain connected over or under a peripheral portion of each guide roller between either a stationary mast section and a movable mast section containing the next cylinder or between the forward most cylinder and movable mast section in the set and the vertically movable fork lift carriage. The machine of Ehrhardt, et al. includes a cluster of three hydraulically and mechanically interconnected cylinders, all of which operate in unison, although the arrangement readily permits removal of individual cylinders from the cluster for servicing and replacement as necessary.
None of these or other known prior art machines utilize a primary cylinder hydraulically connected to one or more secondary lifting cylinders to operate the lifting cylinders in unison to obtain an output lifting force which is substantially greater than an input force needed to actuate the primary cylinder to, in turn, operate the secondary cylinder(s). Moreover, none of these prior art machines uses a primary cylinder connected hydraulically to one or more secondary cylinders in such a manner as to not only obtain an output lifting force which is a multiple of the input force needed to operate the primary cylinder, but also to permit repetitive operations of the primary cylinder in order to lift the secondary cylinder(s) in successive increments to allow use of lifting cylinders of increased total piston chamber volume over that of the primary cylinder chamber and, thus, increased lifting cylinder piston rod length and stroke distance.
By means of our invention, these and other shortcomings of prior art lifting machines are substantially eliminated.